Bleaching of pulp



Patented Mar. 19, 1-929.

- UNITED STATES PATENT OFFICE.

1.11m BRAD EY. or mon'rcma, NEW .fEasEY, AND EDWARD r. mcxnnrn, or NEW ear, 1:. Y. c

Ban-Ammo or PULP.

I No Drawing.

This invention relates .to an improved method of. bleaching wood pulp, produced from wood by chemical processes.

' The bleaching of chemical wood pulp is commonly eflected with a solution of bleaching powder or calcium hypochlorite, but this method of bleaching, as commonly practised,

- not only requires a considerable amount of the bleaching agent, but generally employs 1 an elevated temperature to bring about effective bleaching. In order to bleach the pulp satisfactorily in this way, the action of v the bleaching agents upon the fibre may be sufliciently severe to injure the fibres, with production of oxidation products, 'e. g., oxycellulose, or'with more or less profound modification of part of the cellulose of the fibres,

e. g., with resulting increase in beta andgamma cellulose etc.

The present invention relates to an 1m- 1 proved method of bleaching wood pulp wh ch can be carried out without objectionable mjury to the fibres, and with an important economy in the amount of bleaching agents 26 required, as well as with other advantages such as those hereinafter referred to.

We have found that the bleaching of certain kinds of chemical pulp can advantageously be effected by subjecting the pulp to a preliminary acid treatment, and then subjecting the'acid treated pulp, preferably after washing, to a bleaching treatment with a bleaching agent.

The new rocess is of more or less general 5 application ut is of particular value for the treatment of pulp producedby alkaline cooking processes, that is, chemical-pulp making processes in which the cooking liquor 1s alkaline in character, e., g., the ordmary soda 4o process so called, or the ordinary sulphate process so-called. It is also of part1cular value in the bleaching of pulp produced with a cooking liquor containing essentially normal sodium sulphite as the cooking reagent, or containing a mixture of caustic soda and sodium sulphite in varying proportions, but with an amount of caustic soda such that the fibres of the pulp are not injured to any considerable degree during the cooking op eration.

The following more detailed description a will further illustrate the invention as applied to the bleaching of pulp made by cooking jack-pine with a cooking liquor contain- Application filed March 11;, 1922. Serial No. 514,321.

ing a-preponderating amount of caustic soda together with a lesser amount of normal sodium sulphite equal to about one-fourth of the caustic soda in sodium content, the cooking operation being carried out at a steam pressure of 105115 lbs. and a corresponding temperature for a period of 4 to 6 hours, at

fsaid pressure, and the cooking liquor containing -55 grams per liter of caustic soda and 2?;20 grams per hter of normal sodium sulp ite. i

The pulp was first treated with a dilute solution of hydrochloric acid containing about .5 to 1.0 per cent of hydrochloric acid, and

using 10 pounds of the acid per hundred pounds of pulp (figured on an air dried basis). The pulp was intimately mixed with the dilute acid solution and heated for about 15 minutes to a temperature not exceeding 200 degrees F after which it was washed to remove the greater part of the acid solution and any constituents dissolved therein.

The acid treated pulp was then bleached with a bleaching powder. solution containing 20 lbs. of bleaching powder per hundred pounds of pulp (air dried basis), the bleaching powder being added in the form of a solution of usual strength used in the art of bleaching wood pulp, the solution being suflicient to maintain an alkaline reaction throughout the bleaching operation. The preliminary acid treatment of thepulp enabled the amount of bleaching agent to be reduced and alsoenabled the bleaching operation to be carried-out in a less time and at a lower temperature. The pulp was never theless bleached to a good white strong pulp.

In a similar way, we have bleached pulp from jack-pine (after freeing it from residual liquors and subjecting it to the usual washing operation) by a preliminary acid treatment with a dilute solution of sulphuric acid withheating for a few minutes, then removing the greater part of the solution and washing, then bleaching with calcium hypochlorite or bleaching powder, and with the resulting production of a good strong white 111 p file invention is.also applicable to other pulp, and particularly to pulps which may be diificult to bleach with bleaching powder alone. v

While we do not wish to limit ourselves by any theoretical explanation of the action which takes place in the two-stage bleaching process of the invention, nevertheless the improved results obtained suggest that the prelimin'ary acid treatment removes from the fibres certain compounds of an alkaline char-,

acter, or of an acid soluble character,.which I would otherwise remain present and perhaps interfere with 'or retard the action of the hypochlorite, so that, after the removal of these compounds, the alkaline hypochlorite solu-v tion can, more eflectively do its work. 7

In the followin claims by the term an I alkaline h-ypochlorite solution:we mean that this bleaching stage is carriedout with a bleach liquor which remains alkaline until the bleaching operation has been concluded.

We claim: 1. The method of bleaching chemical wood pulp, resulting from the cooking of the wood with a cooking liquor containing sodium compounds, which comprises subjecting-the pulp first to a preliminary treatment with dilute acid and subsequently to treatment with an alkaline hypochlorite solution.

- 2. The method of bleaching chemical wood pulp, resulting from the cooking of the wood with a cooking liquor containing sodium compound, which comprises subjecting the pulp. first to a preliminary treatment with dilute mineral acid with heating of the pulp durmg such treatment and subsequently to treatment with an alkaline hypochlorite solution.

3. The method of bleaching wood .pulp

I which-comprises subjecting the pulp first to a reliminary treatment with dilute hydrochlbric acid and subsequently to treatment with an alkaline hypochlorite solution.

q 4. The method of. bleaching wood pulp which comprises subjecting the pulp first to a'- reliminary treatment with about to 1% ydrochloric acid in the proportion of one part of acid to ten parts 0 the pulp figured as air dried pulp and subsequently to r treatment with a hypochlorite solution.

5. The method of bleaching chemical pulp, resulting from the cooking of wood with alkaline cooking liquors, which comprises subjecting the pulp to a reliminary treatment with a 'dilute acid so ution, separating the solution from the pulp, and subsequently treating the pulp with an alkaline hypo-, chlorite solution. a

6. The method of bleaching chemical ul resulting from the cooking of wood wit a? kaline cookin "liquors, which comprises subjecting the pn p to a preliminary treatment.

with a dilute mineral acid solution, separati'ng thesolution from the pul quentl treating the pulp with hypoc lorite solution.

7. he method of bleaching chemical pulp,

an alkaline I resulting from thecookin'g of wood with alkaline cooking liquors, which comprises subjecting the pulp toa preliminarytreatment with :a dllute hydrochloric acid solution,

and subseseparating the solution from the pulp, and su sequently line h'vpoch orite solution.

8. The method of bleaching chemical pulp resulting from the cooking of wood with alkaline cooking liquors which comprises .subjecting the pulp to a preliminary treatment with a to 1% h drochloric acid solution 'inthe proportion 0 one part acid to ten parts of pulp figured as air dried pulp,

separating the solution from the pulp, and

su sequently treating the pulp with a hydrochlorite solution. 1

. jecting the pulp first to a preliminary treatment with dilute mineral acid with heatin of the pulp during such treatment, and su e- 9. The method of bleaching coniferous treating the pulpwith an alkaquently to treatment 'with a hypochlorite solution.

11. The method of bleachin coniferous wood pulp which comprises su jecting the pulp rstto a preliminary dilute hydrochloric acid'and substantially to treatment with an alkaline hydrochlorite solution.

12. The method of bleaching chemical pulp, resulting from the cooking of in'e wood with alkaline cooking liquors, w 'chcom-- prises subjecting the pulp to a'preliminary treatment with a dilute acid solution, separating the solution from the pul and subsequently treating the pulp wit a hypochlorite solution.

' 13. The 'method of bleaching chemical pulp, resulting from the cooking of pine wood with alkaline cooking liquors, which comtreatment with v prises subjecting the pul to a preliminary treatment with a dilute mineral acid solution, sefggrating the solution fromthe pulp, and su equently treating the pulp with a hypochlorite solution.

14. The method of bleaching chemical pulp, resulting from the cooking of pine wood I with alkaline cooking liquors, which comprises subjecting the pulp to a. preliminary treatment with a dilute hydrochloric acid s0 lution, separating the solution from the ulp,

and subsequently treating the pulp with a hypochlorite solution.

15. Themethod of bleaching chemical pulp, resulting from the cooking of ine wood with alkaline cooking liquors, w ich'com; prises subjecting the pulp to a preliminary treatment with 5% to 1% hydrocloric acid solution, separating the solution from the pulp, and subsequently treating the pulp with bleaching powder alone, which pulp results from the cooking of wood with chemical cooking liquors containing sodium compounds, which comprises subjecting the pulp to a preliminary treatment with a dilute min eral acid solution, separating the solution CERTIFICATE Patent No. 1,705,897.

from the pulp, and subse uently treating the pulp with an alkaline ca cium hypochlorite solution.

18. The method of bleaching chemical pulp resulting from the cooking of wood with a cooking liquor containing a sulfite of sodium, which comprises subjecting the pulp to a preliminary treatment with a dilute mineral acid solution, separating the solution from the pulp, and subsequently treating the pulp with a hypochlorite solution.

19. The improvement in the bleaching of chemical pulp with an alkaline hypochlorite solution, which comprises subjecting the pulp to the action of a hot dilute mineral acid prior to the bleaching o eration.

In testimony w ereof we afiix our signatures.

LINN BRADLEY. EDWARD P. MoKEEFE.

or CORRECTION.

Granted March 19, 1929, w

LINN BRADLEY ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, l ne 77, claim 8, for the syllable "hydro-' read "hypo-", line 99, claim 11, for the word "hydrochlorite read "hypochlorite", and line 129, claim 15, for the word I "hydrocloric'lread "hydrochloric"; and that the said Letters Patent should be read with these corrections therein that the same may of the case in the Patent Office.

conform to the record Signed and sealed this 30th day of April, A. o. 1929.

(Seal) M. J. Moore, Acting Commissioner of Patents,

CERTIFICATE OF CORRECTION.

Patent No. 1,705,897. Granted March 19, 1929, to

LINN BRADLEY ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 77, claim 8, for the syllable "hydro-" read "hypo-", line 99, claim. 11,.. for the word "hydrochlorite" read "hypochlorite", and line 129. claim 15, for the word "hydrocloric" read "hydrochloric"; and that the said Letters Patent should be i read with these corrections therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 30th day of April, A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

